Author: Dongsheng Cai
MDL-71330 mod_chat: Implement the activity dates functionality
http://git.moodle.org/gw?p=moodle.git;a=commit;h=f628b3d1bd6ab730b1b31ce985ccb889d6324d06
http://github.com/moodle/moodle/commit/f628b3d1bd6ab730b1b31ce985ccb889d6324d06
+ 3.11 en [nextchattime,mod_chat]
+ 3.11 en [sessionstartsin,mod_chat]